1. Field of the Invention
The present invention relates to an electrolytic capacitor, and particularly to an electrolytic capacitor having anode and cathode members and the like that are wound together.
2. Description of the Background Art
At present, attention has been given to electrolytic capacitors that use electrically conductive polymer materials such as polypyrrole, polythiophene, polyfuran or polyaniline, or TCNQ complex salt (7,7,8,8-tetracyano-quinodimethane). In this kind of electrolytic capacitor, a capacitor element is formed of anode and cathode foils that are wound together with a separator interposed therebetween, and is housed in a casing of aluminum. Aluminum foil provided with a dielectric oxide film is used as the anode foil, and aluminum foil is used as the cathode foil.
The anode and cathode foils and the like of the conventional electrolytic capacitor employing the above aluminum foils are wound as follows. As shown in FIG. 6, anode and cathode foils 140 and 141 as well as two belt-like separator paper sheets 106 and 107 each having a predetermined length are prepared. These are arranged such that one separator paper sheet 106 is interposed between anode and cathode foils 140 and 141, and anode foil 140 is interposed between one and other separator paper sheets 106 and 107. Anode and cathode leads 151 and 152 that will form anode and cathode terminals in the completed electrolytic capacitor are connected to anode and cathode foils 140 and 141 through lead tab terminals 150.
Then, as shown in FIG. 7, ends on one side of anode and cathode foils 140 and 141 as well as separator paper sheets 106 and 107 thus arranged are pinched between cores 131a and 131b, and cores 131a and 131b pinching them are turned in a predetermined direction so that anode and cathode foils 140 and 141 and others are wound up from the one end to form a capacitor element 102 as shown in FIG. 8.
In the solid electrolytic capacitor using the electrically conductive polymer material such as polypyrrole, polythiophene or the like, it is required to reduce an ESR (Equivalent Series Resistance), and demands for the electrolytic capacitors of the low ESR are rapidly increasing. However, further reduction in ESR will soon be limited in the electrolytic capacitor (wound-type electrolytic capacitor) formed by winding up the anode and cathode foils and others.
As a wound-type electrolytic capacitor meeting such demands of a market, the inventors and others have proposed an electrolytic capacitor employing a plurality of anode foils. The electrolytic capacitor having the plurality of anode foils has a plurality of anode leads and thus has multiple terminals. For example, when the electrolytic capacitor has the two anode leads, it also has two cathode leads so that the four leads in total are connected to the capacitor element.
Particularly, as compared with the two-terminal structure, the multi-terminal structure is further restricted in position of the lead tab terminal attached to the anode foil or the like, in connection with the leading or guiding position of the lead tab terminal and the manner of winding. This will be described below.
In the electrolytic capacitor of the two terminals, the position where the lead tab terminal is located in the capacitor element after the winding processing depends on the position where the lead tab terminal is connected to the anode foil. Therefore, it is difficult to change the position of connection of the lead tab terminal. For example, as shown in FIG. 9, when a anode foil 161 is to be wound from it one end A and anode foil 161 has a length C (e.g., about 120 mm), a position 163 where the lead tab terminal is attached is at a distance B of about 30 mm from one end A.
Then, it is assumed that the multi-terminal electrolytic capacitor employs two anode foils. FIG. 10 shows an ideal arrangement for suppressing the ESR to the maximum extent in this case. In this arrangement, two anode foils 161a and 161b have the same size (C/2), and positions 163a and 163b where the lead tab terminals are attached are located near longitudinally central positions of anode foils 161a and 161b, respectively.
As shown in FIG. 11, when the winding of anode foil 161a starts from its one end A, position 163a where the first lead tab terminal is connected must be at a distance of about 30 mm from one end A, in view of the pitch of the lead tab terminals and the positional relationship between them after the winding. Also, position 163b where the second lead tab terminal is connected must be at a distance of about 6 mm from position 163a where the first lead tab terminal is connected. Therefore, when two anode foils 161a and 161b have the same size, the two lead tab terminals are connected to one anode foil 161a, and no lead tab terminal is connected to other anode foil 161b. 
For overcoming the above, the first lead tab terminals may be connected to the one anode foil, and the second lead tab terminal may be connected to the other anode foil. In this case, as shown in FIG. 12, two anode foils 161a and 161b must have different lengths D and E, respectively, and one and other anode foils 161a and 161b must have length D from about 35 mm to about 45 mm, and length E from about 85 mm to about 80 mm, respectively. As described above, when the multi-terminal structure employs the manner of starting the winding from one end of the anode foil, the foregoing ideal arrangement cannot be employed due to restrictions on the positional relationship between the first and second lead tab terminals.
For overcoming the above problem, the inventors and others have proposed, in Japanese Patent Laying-Open No. 2007-173773, a manner of winding foils and others (anode foils 103 and 104, a cathode foil 105 and separator paper sheets 106 and 107) that have predetermined lengths and are located in predetermined positions, respectively, by starting the winding from their longitudinally central portions. Also, the inventors and others have proposed a manner shown in FIG. 14, in which the winding starting from the longitudinally central portions is performed using cores 131a and 131b with cathode foil 105 located between two separator paper sheets 106 and 107.
In this case, first and second anode leads 111 and 112 are connected to first and second anode foils 103 and 104 through lead tab terminals 150, respectively. Also, first and second cathode leads 113 and 114 are connected to cathode foil 105 through lead tab terminals 150, respectively.